1. Field of the Invention
This invention relates to an electric device in the form of a transformer or an inductor, having a two-part magnetic core; and this invention relates to cross-sectional geometry and resultant shape of a magnetic core part of such a device.
2. Introduction to the Invention
Electrical devices for use as transformers and inductors commonly comprise a magnetic core inserted into a bobbin around which one or more wire coils are wound. When used for power supply, data, or telecommunications applications, such devices are mounted on printed circuit boards (PCBs), along with other electronic elements. Due to the large number of elements present on the board, it is important that the amount of space occupied by the electrical device be minimized. However, it is also important that the electrical device maintain a certain level of performance required for maximum data or power throughput. The conventional approach for reducing the area occupied by the device is to use a smaller conventional part. However, this can give disadvantages in terms of leakage inductance, DC resistance, and total harmonic distortion.
A conventional transformer, such as that disclosed in U.S. Pat. No. 6,483,412 (Holdahl et al.), is positioned so that the core, which has a generally rectangular shape with curved edges, is perpendicular to the PCB, so as to minimize the amount of space used on the printed circuit board. It is typically surface-mounted onto the PCB by means of self-leaded terminals or pins extending from a structure forming a coil bobbin, the terminals or pins being aligned with and bonded to circuit traces or pads of the PCB.
Heretofore it has been assumed by workers in the art, that in shielded core geometries the sidewalls of the skirt and the back plane must extend down the same distance. In addition, it has been assumed that the central core portion of the magnetic core structure should be provided with a symmetrical cross-sectional shape. By “symmetrical” it is meant that the central core portion can be divided into similar halves by a plane parallel to the device mounting plane and passing through a center of mass, i.e., centroid, of the central core portion. For example, U.S. Pat. No. 4,760,366 (Mitsui) illustrates a ferrite core having a central core portion including circular ends and a flattened rectangular central region, rendering the resultant core structure and electrical device relatively wide and thereby unduly consumptive of valuable PCB space. Commonly assigned U.S. Pat. No. 6,483,412 (Holdahl et al), U.S. Pat. No. 6,501,362 (Hoffman et al.) and U.S. Pat. No. 6,696,913 (Meuche et al.) attempted to reduce the PCB footprint of the electrical device by orientating the central core region perpendicularly relative to the PCB mounting plane. In these prior examples the sidewalls of the skirt and the back plane extend downwardly toward the mounting surface or plane by the same distance. Another limitation of these prior art electrical devices is that the central core regions are symmetrical about a plane parallel to the PCB mounting plane and passing through the center of each central core region. While these approaches have resulted in usable electrical devices, the reorientation to vertical of the oblong or flattened symmetrical central core region has necessarily extended the resultant height of the device above the PCB surface, creating issues with regard to adjacent PCB board spacing and mechanical integrity of the surface mounting arrangement.
A hitherto unsolved need has remained for an electrical device having both a reduced footprint and a reduced mounting height above the PCB.